A wake-up lamp is a device comprising a controllable light source of which the light output intensity can be varied between almost zero and a maximum, which maximum in practice may be in the order of 250-400 Lux at the eyes of the user, it being assumed that the distance between the light source and the user's eyes is a fixed value in accordance with the user's manual. The device is typically associated with an alarm clock, and is intended to wake up people in a comfortable and natural manner by simulating sunrise (or dawn). Starting at a predefined advance time before the set alarm time (typically about 30 minutes earlier), the light source switches on at low intensity, and its intensity is gradually increased until at the alarm time the maximum intensity is reached. Wake-up lamps are known in practice, therefore a further explanation is not needed.
In a simple embodiment, the intensity increase of a wake-up lamp is achieved by simply increasing the power supplied to the light source. Depending on the type of light source, this can be done by increasing the supply voltage (for instance in the case of an incandescent lamp), or it may be necessary to use a more complicated driver design (for instance in the case of an LED). However, the increase of light intensity is only one of the aspects of a successful wake-up lamp. Another important aspect is the colour of the output light. In people's perception, the natural sunrise is associated with a colour change from deep red to yellowish white as the light intensity increases. State of the art wake-up lamps do not show such colour variation, and the result is perceived as “unnatural”.